Opening device for a double-locked stitch



April 17, 1962 R. E. SCHANZLE 3,030,003 OPENING DEVICE FOR A DOUBLE-LOCKED STITCH Filed Nov. 24, 1959 7 9 /7 /9 I r /a /5' /9 7/11 m I 20 gwmw,

INVENTOR. Ems/e A. Sex/Anna,

ATTQ 2 N EY- Waited htates This invention relates to a device for opening sewed bags; more particularly, it pertains to a pull tab for a double-locked stitch and a method of applying same.

There are many products packaged in bags today. Usually the bags are sewed across the top to provide a secure closure. Almost all sewed bags in commercial use have one of two well known top closure stitches; either a chain stitch employing one thread or a double-locked stitch employing two threads. The chain stitch is fairly easy to open. It is only necessary to find and pull the end of the thread on the side opposite the loops in order to unravel the chain stitch. On the other hand, the doublelocked stitch has two threads and almost invariably these threads become entangled at their free ends. Sometimes, this is even done purposely to prevent accidental opening of the bag. This makes it necessary to first disentangle the threads and then select and pull on the proper thread to unlock the stitch in order to unravel it. If the wrong thread is selected, it will only tend to make the stitch more difficult to open. It is not at all uncommon to find a bag with a double-locked stitch in which the two threads are so entangled that it takes considerable time and patience to disentagle them before the bag can be opened without cutting or slicing the bag itself. Thus, at times the opening of a bag with a double-locked stitch can be very exasperating and time consuming.

An object of this invention is a device for eliminating the difiiculties sometimes encountered when opening bags having a double-locked stitch.

Another object of this invention is the provision of an opening device for a double-locked stitch which prevents the two threads from becoming entangled; the opening device also prevents accidental opening due to unraveling of the threads which form the stitch.

Still another object of this invention is the provision of a method for applying a pull tab to the locking thread of a double-locked stitch.

Briefly stated, in accordance with one aspect of the invention, a bag having its closure sewed with a doublelocked stitch has a pull tab adhered to the locking thread by first cutting the sewed closure at a point intermediate the ends of one loop of the needle thread and thereafter adhesively securing the pull tab to the cut end of the stitch on the side having both threads. The pull tab prevents entanglement of the two threads. At the same time, the tab can be used as an opening device since the character and physical lengths of the threads gives the tab a greater adherence to the locking thread whereby it provides an opening tab when pulled for unlocking the stitch and permitting the closure to be opened.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter regarded as forming the present invention, it is believed the invention will be better understood from the Latent following description taken in connection with the accorn- 3,630fih3 Patented Apr. 17, 1962 ice Referring to the drawings and particularly FIGURE 1, i

there is shown one method of closing the tops of a series of empty bags in order to prepare them for application of the tear tab of this invention. Normally, the bags would first be sewed'closed across their tops as shown. After being separated and having the tear tab attached, the individual bags are then filled through the bottom and then sealed on the bottom as by sewing, stapling, gluing or the like. The invention can also be practiced, of course, with filled bags that are closed across the top as a last step. However, the bottom filling procedure is described here as a convenient way of practicing the instant invention.

The empty bags 10, 11 and 12 have the top portions of their walls superposed so that a tape 13 can be folded over the outer edges of the bag walls. The tape 13 is then sewed continuously by a conventional sewing head to provide a continuous stitch 14. The bags are separated by cutting the tape 13 intermediate the bags 10, 11 and 12 as at 15 and 16. While a tape-bound closure is shown for illustrative purposes, the invention is also applicable to plain sewed closures, folded top closures and others as will be appreciated by persons skilled in the art.

A detailed cross-section of the stitch 14 is shown in FIGURE 2. The stitch is a conventional double-locked stitch composed of a needle thread 17 and a locking thread 18. For simplicity of illustration, the views of FIGURES 2, 3 and 4 have been taken between bags 10 and 11 so that only the walls 19 and 2th of the tape 13 are shown as being sewed together. Of course, Where the tape 13 is contiguous to the bag Walls, there will be a plurality of layers of paper between the walls 19 and 20.

Before a pull tab is applied to the locking thread 18, the tape 13 and stitch are severed at 15 as shown in FIGURES 1 and 3. An important aspect of this step is that it must be done intermediate the ends 21 and 22 of a loop 23 in the needle thread 17. This causes the severed end 24 of the locking thread 18 to protrude outwardly, as shown, and allows the pulltab to be applied before the end 24 of the locking thread and the ends 25 and 26 of the needle thread become entangled.

As shown in FIGURE 4, the pull tab 27 is applied over the severed ends of the stitch lying to the right of the cut 15 of FIGURE 3. It is important that the pull tab be applied to the end shown. It will not function if applied to the other end of the seam because the double-locked stitch can only be opened by pulling on the locking thread 18 in a direction opposite to'the direction in which the stitch was sewn. The direction of sewing is always in the direction pointed by the end 21 of each loop 23 of the needle thread 17.

The pull tab 27, as aforesaid, prevents entanglement of the severed ends of the two threads while simultaneously being available as a means for opening the bag when attached to the end 24 of the locking thread 18. The pull tab 27 also prevents accidental unraveling of the seam due to its adherence to the locking thread 18. In a preferred construction, the pull tab 27 is substantially wider than the stitch 14 so that it can be adhered to the Wall 20 on either or both sides of the stitch 14. In addition, the pull tab 2'7 preferably is of sufficient length to extend beyond the end of the wall 2! in order to provide a free end 28 for the convenience of a user. The other end of the pull tab 27 may extend back on the tape 14 to cover several loops 23 of the needle thread as shown on the drawing. The surface 29 of the pull tab 27 is coated with an adhesive, preferably pressure sensitive although glue or other kinds of adhesives may be used. The free end 28 can be folded over on itself in order to prevent the exposed adhesive surface 29 from becoming accidentally adhered to some foreign object.

Ordinarily, the adhesive surface 29 of the pull tab 27 will have greater adherence to the severed end 24 of the locking thread 18. It has been discovered that when the tab 27 is pulled, it will tend to remain adhered to the locking thread 18 while simultaneously being stripped from the ends 25 and 26 of the needle thread as well as the adjacent loops 23 of the needle thread 17.

In order to be assured that the pull tab 27 will function properly, it is preferable to use a locking thread having a greater affinity for the adhesive surface 29 of the pull tab 27 than the needle thread 17 has. This can be accomplished by the use of a plastic needle thread 17 or by coating the needle thread 17 with wax, plastic or similar substances to give it reduced adherence characteristics to the adhesive surface 29. Thus, when the pull tab 27 is pulled away from the wall 20 of the tape 13, it will remain adhered to the end 24 of the locking thread 18 and act as a convenient opening means.

FIGURE illustrates the bag 11 after being filled with product and closed on the bottom as by sewing, stapling, gluing or the like. The unlocking action caused by pulling on the free end 28 of the tab 27 is shown in FIGURE 6 wherein a partially opened bag is illustrated. The stitch becomes completely unlocked by removing the locking thread 18 for its entire length thus giving access to the interior of the bag.

While particular embodiments of the invention have been illustrated and described, it will be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention and it is intended to cover in the appended claims all such changes and modifications that are Within the scope of this invention.

What is claimed as new is:

1. An opening device for a bag having its closure sewed together by a double-locked stitch composed of a needle thread and a locking thread, both threads of said stitch being severed intermediate the ends of an exposed loop of the needle thread, a pull tab having an adhesive coated surface adhered to the severed ends of said threads, including said locking thread, at the end that was sewed last and on the wall contiguous to said stitch to prevent entanglement thereof, said pull tab being adhered to said locking thread so that when pulled it serves as an unlocking device for said stitch to allow opening of said bag closure.

2. An opening device for a bag having its closure sewed together by a double-locked stitch composed of a needle thread and a locking thread, said needle thread having reduced adherence characteristics to adhesives as compared to said locking thread, a pull tab having an adhesive coated surface adhered to the end of said stitch that was last sewed and on the wall contiguous to said stitch in order to prevent entanglement of the said threads, said pull tab having greater adherence to said locking thread than to said needle thread so that when pulled it serves as a means for initiating unlocking of said stitch to allow opening of said bag.

3. An opening device for a bag having its closure sewed together by a double-locked stitch composed of a needle thread and a locking thread, said needle thread having reduced adherence characteristics to adhesives as compared to said locking thread, said stitch being severed intermediate the ends of an exposed loop of the needle thread, a pull tab having an adhesive coated surface adhered to the severed ends of said threads at the end that was sewed last and on the bag wall contiguous to said stitch in order to prevent entanglement and accidental unraveling thereof, said pull tab having greater adherence to said locking thread than to said needle thread to serve as a means for initiating unlocking of said stitch to allow opening of said bag.

4. An opening device as claimed in claim 3 in which the pull tab is a short piece of pressure sensitive tape.

5. An opening device for a bag having its closure sewed together by a double-locked stitch composed of a needle thread and a locking thread, a pull tab coated on one surface with an adhesive and placed so that the adhesive surface overlies and adheres to the end of said stitch that was sewed last, including the ends of said threads which are severed after completing said stitch, said pull tab preventing entanglement of the severed ends of the locking thread and needle thread, said pull tab adhering to said threads sutficiently so that when pulled it acts as a means for freeing said locking thread to unlock the stitch and open the bag closure.

References Cited in the file of this patent UNITED STATES PATENTS 2,945,615 Swanson July 19, 1960 Williams et al Apr. 4, 1961 

